This invention relates generally to large bearings with rolling elements and, more particularly, to bearing retainers for rolling element bearings operated at very low rotational speeds.
A bearing retainer in a rolling element bearing serves to separate and align the rolling elements and may also restrict radial movement of the rolling elements. If the bearing retainer restricts the rolling elements both radial directions, the bearing retainer is also known as a bearing "cage." In large bearings with rolling elements, i.e., bearings having a diameter greater than 0.5 meters, the bearing retainer is made very rugged for reliable service and to sustain loads during lifting that is required for installation and removal of the bearing retainer and rolling elements.
Surface damage commonly occurs in large bearings with spherical, tapered and cylindrical rolling elements that are operated at very low rotational speeds. Due to lack of sufficient centrifugal loading to maintain spin velocity of rolling elements, rolling elements slide or skid against the outer raceway of the bearing during part of their orbit of the bearing. Specifically, centrifugal loading is not adequate to assist in the separation of the surfaces with hydrodynamic or elastrohydrodynamic films. Such surface damage may act as points of initiation of fatigue cracks and may severely limit the service life of bearing components.
Another problem occurs because these large bearings are typically mounted with loose or transition fits when installed in large equipment. In addition, radial internal clearance within the bearings is often desired in such applications to provide ease of installation of bearing elements and to accommodate expected thermal differentials. As a result of these clearances, the rolling elements of the bearings are loaded for only a portion of their orbit of the bearing. Frictional forces within the bearing and lack of traction of the rolling elements due to normal load at the raceway contact cause the rolling elements to lose spin velocity, resulting in surface damage when raceway contact is reestablished.
Previous proposals to reduce such surface damage have focused primarily on improved lubrication. For example, various coatings for the retaining pins have been proposed to reduce drag between the retaining pins and the rolling elements. Other proposals have attempted to improve lubricant entry to the rolling elements, have suggested special treatment of bearing raceways and rolling elements to reduce wear, or have considered use of small clearances and traction fluids. However, none of these proposals has been successful in solving the underlying problem.
The foregoing illustrates limitations known to exist in present bearing retainers for large bearings with rolling elements. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.